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Molluscan ornament in modern oceans increases with decreasing latitude, in response to greater risk from tropical durophages (shell-crushing predators). The latitudinal gradient is presumed to be associated with the appearance of modern durophages during the Cretaceous, but this is untested. A radiation of durophages during the Devonian may have resulted in sufficient predation pressure to influence prey distribution similarly, although Devonian predators and prey are distantly related to their recent equivalents. This study examines latitudinal variation in ornament in Devonian strophomenide brachiopods to determine if a latitudinal gradient existed. A latitudinal gradient is documented for the Devonian; ornament decreases with increasing latitude. The correlation between proportion of spinose genera and region is -0.947 (p < 0.001). Similar to modern molluscs, spinose strophomenide genera constitute 26%-41% of tropical genera. The data corroborate the hypothesis that predation influenced the evolution and distribution of prey as early as the Devonian Period.

The fixosessile, perireefal to reefal Devonian epibiont Davidsonia cemented itself by its entire ventral valve to the underside of alveolitid tabulate corals, or to stromatoporoid sponges. It occupied a cryptic niche in perireefal biostromal thickets to reef complexes in the Old World faunal realm (Europe, western North America), and Uralian-Central Asian faunal province. A new species, D. septata, is here reported in abundance for the first time from Middle Devonian (Givetian) rocks of Yunnan, thus extending its range to South China. The usual absence of the brachial valve is suggested to be due to postmortem taphonomy as a result of its unique, cemented mode of life on the undersides of corals or sponges. A new genus of coarsely ribbed, partly libero-, partly fixosessile davidsoniid, Rugodavidsonia, type Davidsonia woodwardiana (DeKoninck), mimicking unrelated Late Paleozoic orthotetids, is also described, demonstrating that ribs evolved secondarily in a family dominated from its inception by smooth shells. Its paleogeographic distribution ranged from Europe through western North America (and possibly China), commonly accompanying Davidsonia in similar assemblages, but with a slightly different mode of life. Reexamination of available material, using thin sections, peels and SEM, confirms that the impunctate shell structure, dorsally directed spiralia, nature of the hinge mechanism, the deltidial plates, absence of a chilidium, 'atrypoid' musculature and vascular markings, show features in Davidsonia and Rugodavidsonia that are all typical of the Order Atrypida. Thus, Davidsonia demonstrates that ventral valve cementation evolved independently more than once in articulate brachiopods such as strophomenids, productids, atrypids, and thecideid spiriferids. A revised classification of the Davidsonioidea and Palaferelloidea is proposed. Relationships between various genera are outlined in a new family tree for these groups. The various families discussed, including the Symmatrypidae, are united under a new suborder, the Davidsoniidina, a primarily carbonate platform and perireefal dwelling group, which first evolved during the Ludlovian (Late Silurian) in the Uralian-Central Asian tropical shelf region, diversified over a period of [approximately]47 Ma, and then died out during the late Givetian, 10 Ma prior to the Frasnian-Famenian mass extinction events.

Fossiliferous marine Devonian has been known in Chile for less than a decade. The initial discovery from south of the Salar de Atacama region, in the Sierra de Almeida, northern Chile is described together with its brachiopods. The brachiopods indicate an age span of Emsian-Eifelian or Givetian, shallow-water conditions in the Benthic Assemblage 2 range, and a biogeographic boundary region between the cool climate Malvinokaffric Realm and warmer region extra-Malvinokaffric Realms, including the Eastern Americas Realm and the Rhenish-Bohemian Region of the Old World Realm. The recent discovery of a Malvinokaffric Realm trilobite far to the south in Chile, at Buill in the Andes of Chiloe, serves to underline our very preliminary knowledge of the Chilean Devonian, whereas the alleged Devonian brachiopods from the Chonos Archipelago far to the south are probably bivalves of uncertain age.

The component subfamilies of the Delthyridoidea are critically reviewed and subjected to phylogenetic analysis. This shows the presence of two clades, assigned to the Delthyrididae and Acrospiriferidae, within the superfamily. The subfamilial categories are redefined mainly on the basis of the characters used in the phylogenetic analysis. The spiriferid, mainly delthyridide, Gaspe fauna is formally revised and redescribed. This new taxonomic treatment leads to more precise biostratigraphy and to the recognition of a new subfamily, the Gaspespiriferinae, based on the new genus Gaspespirifer. Five new species are described: Howellella (Howellella) forillonensis, Brachyspirifer (Brachyspirifer) briseboisi, Paraspirifer desbiensi, Brevispirifer florentinus, and B. quebecensis, The occurrence of Brevispirifer species with Middle Devonian chonetaceans confirms the presence of marine Eifelian strata in the Matapedia Valley. Paraspirifer desbiensi n. sp. and two species left in open nomenclature, Vandercammenina sp. and Mucrospirifer sp., have considerable biostratigraphic and biogeographic significance in the Lower Devonian. The first occurrence in the Eastern Americas Realm of the typically Rhenish genera Brachyspirifer, Paraspirifer, and Vandercammenina are in Gaspe. This reinforces the hypothesis that Gaspe served as a stepping stone for Rhenish species invading North America in Pragian and Emsian times, as previously suggested by bivalve biogeography.

A growth series of Stringocephalus gubiensis, described here, reveals that the cardinal process of Stringocephalus originated from a bilobate structure, and the growth of its dorsal median septum is highly related to cardinal process development. From this observation we conclude that Kaplex is, structurally and temporally, a suitable ancestor for Stringocephalus, with Bornhardtina ancestral to Kaplex. Subfamilial classification of the family Stringocephalidae is revised based on the presence or absence of median septa and the nature of hinge plates as well as on cardinal process formation. The Kaplexinae and Omoloninae are proposed as new subfamilies, with the Kaplexinae, including Kaplex and Erectocephalus, and the Omoloninae, including Omolonia, Kumbella, and Hemistringocephalus. Morphologic study of South China and Western Canadian Stringocephalus reveals that late forms of the genus tend to have a higher dorsal septum and more complex cardinal process than the early forms. In view of functional morphology, these trends reflect functional perfection of the cardinal process build-up and the lever system for improving the efficiency of opening and closing the shell.